To my knowledge only Yugo's (M70 for example) used them. They are easy to spot by their bulged sides vs the flat sides of a normal trunnion, which requires a receiver specifically designed for them.
As to why, I assume that it was done for some perceived advantage in strength since they were used with a 1.5mm receiver, probably because they had GLs

THE M70 USES PRETTY MUCH THE SAME TRUNION AS A YUGO RPK. IT IS HEAVIER OVER THE LUGS AN IS ARGUAbLE A STONGER PIECE IN EVERY AREA OF ITS CONSTRUCTION BOTH IN STENGTH AN IN WEIGHT . i

It is of little importance IMO on a 7.62x39 or 223 weapon as a standard akm trunion is plenty strong .

Unless you really think you need a baynet for zombies or you want the cool mall ninja effect Id skip the bayo an buy ammo with the money . if there is a simular gun that uses the same ID GB an the GB in yours is in the correct locsation Is likely doable . does your gun haver a gas shut off GB for gernade launching ?